1. Technical Field
The present invention relates to an apparatus for detecting a rollover of a vehicle and an apparatus for activating occupant protective devices.
2. Related Art
Recent vehicles are frequently required to have a variety of safety devices for occupants. One of such devices is safety devices, such as pretensioners and shock absorbing airbags. These devices are very helpful for occupants when the vehicle makes a rollover or an overturn due to various reasons.
A variety of techniques for determining such a rollover, which is absolutely necessary for activating the occupant protective safety devices, has been proposed at present, as can be seen from Japanese patent-laid open KOKAI (unexamined) Nos. 7-164985 and 2001-260780.
The former proposes how to determine a turnover of a vehicle. According to this determination technique, an inclination angle of the vehicle and an inclination angular velocity thereof are detected to determine a vehicle's turnover using a relationship between the inclination angle and the inclination angular velocity. If this determined result reveals a possibility of causing the turnover, one or more occupant protective devices mounted on the vehicle are activated immediately.
However, this determination technique is still unsatisfied as described below. Though the rollover of the vehicle can be classified into many types in terms of their causes, one type is a rollover called “flip-over,” in which wheels on one of the right and left sides of a vehicle run on an obstacle so that the vehicle makes a rollover. In this case, the vehicle rolls over at a faster speed, it is absolutely necessary to activate the occupant protective device(s) in an early stage during the rollover. However, in such an early stage, the inclination angle is still low. Hence, this conventional determination way concludes that the vehicle inclination in progress at present will not result in a rollover, whereby it is very difficult to activate the occupant protective device(s) in an early and proper timing during the rollover.
Of the foregoing prior art references, the latter (No. 2001-260780) provides how to determine whether or not there is a possibility that a vehicle will make over. This reference shows a two-dimensional map that uses two parameters consisting of a roll angle of a vehicle and a roll angular velocity thereof. Threshold lines are set on the map so as to form non-rollover regions showing non-rollover and rollover regions showing a possible rollover. Whether or not a history line defined by a roll angle and a roll angular velocity of a vehicle crosses one of the threshold lines from the non-rollover region to the rollover region shows whether or not that is a possibility of causing a vehicle's rollover, respectively. This determined result is then reflected in control of deploying air curtains and/or side airbags.
Furthermore, this rollover determination makes the threshold lines move in response to an increase in a side skid speed of the vehicle. This festinates the timing to start the deployment to protect the occupant in a trip-over. However this start timing is not always proper.
For example, assume that a vehicle whose height is high, such as SUV (Sports Utility Vehicles) crashes into a side of a parked vehicle. In such a case, a rollover may be caused, which is called “SUV side-impact originated rollover.” In this rollover, the crashed vehicle makes a roll around axis passing the wheels on the non-crashed side immediately after the crash, and no side skid speed is detected. However, an occupant upper body is forced to swing toward the crash side immediately after the crash, so that it is necessary to deploy the driver's side devices such as air curtains in an early stage of the rollover. With regard to protecting the occupant from such rollovers, the foregoing determination based on the conventional map is not totally sufficient in detecting a more proper timing for deploying the safety devices.